The cylinder of your eye, which represents the lens power needed to correct astigmatism, can change. These changes are typically slow and predictable over a lifetime. Astigmatism is a common refractive error that occurs when the eye’s front surface (cornea) or internal lens has an irregular curvature. This irregularity prevents light from focusing on a single point on the retina, causing vision to be blurred or distorted.
Understanding the Cylinder Measurement and Astigmatism
The cylinder value on an eye prescription is measured in diopters and quantifies the difference in curvature between the steepest and flattest meridians of the eye’s focusing surfaces.
The cylinder power works in conjunction with the axis, a number between 1 and 180 degrees, which indicates the precise orientation of the irregular curvature. The axis ensures the corrective lens is aligned correctly. If the cylinder value is blank on a prescription, the astigmatism is either non-existent or too minor to require correction.
Astigmatism stems from two primary sources: the cornea (corneal astigmatism) or the internal crystalline lens (lenticular astigmatism). The cornea is usually the main contributor to the cylinder measurement because it provides the majority of the eye’s focusing power. The corrective lens applies power in a specific direction to neutralize this difference, allowing light to focus sharply on the retina.
Specific Factors That Influence Cylinder Changes
Age-Related Shifts
The primary driver of cylinder change is the natural aging process, which often involves a measurable shift in the astigmatism’s axis over several decades. In young adults, the most common type is “with-the-rule” astigmatism (steepest curve runs vertically). As a person ages, this slowly transitions to “against-the-rule” astigmatism (steepest curve becomes horizontal). This shift is caused by subtle alterations in corneal curvature, potentially due to changes in eyelid tension or modifications to the corneal structure. The change is typically gradual, often beginning after the mid-40s.
Progressive Conditions
Conditions like Keratoconus can cause more rapid and dramatic cylinder changes. Keratoconus is a progressive condition where the cornea thins and bulges outward into a cone shape, creating a significant and irregular increase in astigmatism. A fast-increasing cylindrical power, especially in younger individuals, is a sign that prompts investigation for this condition.
Trauma and Systemic Health
Sudden or significant cylinder shifts can be induced by external factors or systemic health issues. Ocular trauma resulting in scarring can permanently alter the cornea’s curvature. Internal changes, such as the development of cataracts, can alter the shape of the natural lens, changing the cylinder measurement. Diabetes, through blood sugar fluctuations, can also temporarily affect the lens and cause vision changes.
Surgical Intervention
Surgical procedures, such as cataract surgery or LASIK, are a cause of planned or anticipated cylinder changes. During cataract surgery, the removal of the natural lens and insertion of an artificial intraocular lens (IOL) can correct pre-existing astigmatism. Small changes in the cornea’s shape following laser procedures can lead to prescription adjustments.
Tracking and Adjusting Vision Correction
Tracking cylinder changes requires regular, comprehensive eye examinations to accurately monitor the eye’s refractive status. Eye care professionals utilize various diagnostic instruments to measure the curvature of the cornea and determine the precise amount and orientation of astigmatism.
The primary tools include the keratometer, which measures the curvature of the central cornea, and corneal topography, which provides a detailed, three-dimensional map of the entire corneal surface. Corneal tomography is an advanced imaging technique that can detect structural changes before the cylinder power shifts significantly, which is particularly useful for monitoring conditions like Keratoconus.
These objective measurements are combined with a subjective refraction test, where the patient provides feedback while looking through a phoropter, to fine-tune the final prescription.
When a change in the cylinder is detected, it necessitates an update to corrective lenses, whether through new eyeglasses or toric contact lenses, to maintain clear vision. A significant change in prescription is defined as a large enough difference that it noticeably affects visual clarity and comfort. Patients should seek immediate care if they notice a sudden, dramatic blurriness, ghosting, or distortion in their vision, as this can signal a rapidly progressing condition requiring urgent management.